This invention pertains to a method for forming a fine pattern for use in formation of semiconductor devices and integrated circuits on a semiconductor substrate.
Recently, various fine-pattern formation methods have been used in the field of IC and LSI production. As miniaturization in process dimensions has progressed, a process making use of a shortwave light source has been considered one of the most important fine-pattern formation techniques. In a lithography process with the aid of a shortwave light source, a chemically amplified resist is generally used. A chemically amplified resist is composed of a multi-component material containing an acid generator capable of producing acid upon exposure to radiant ray and a compound reactive to acid. Acid catalytic reaction is utilized to change alkali solubilities, whereupon a fine-pattern is formed.
Referring now to FIGS. 4a and 4b, a conventional fine-pattern formation technique will be described below.
As shown in FIG. 4a, TiN film 2 is formed on top of semiconductor substrate 1. TiN film 2 has a basic surface because of the existence of basic substance 3 thereon.
Next, a chemically amplified resist of positive type, e.g., WKR-PT-2 manufactured by Wako Pure Chemical Industries Ltd., is applied to TiN film 2 to form a resist film 4. An exposure step through mask 5, a post-exposure baking step, and a development step are performed on resist film 4 to form resist pattern 6 shown in FIG. 4b.
The aforesaid fine-pattern formation technique, however, suffers from some problems. For example, the phenomenon of footing or scumming occurs so that resist pattern 6 results in having a spread-out bottom. In other words, resist pattern 6 is damaged. Use of a chemically amplified resist of positive type creates such footing or scumming to a resultant resist pattern. On the other hand, use of a chemically amplified resist of negative type creates the phenomenon of under-cutting so that resist pattern 6 results in having an inwardly tapered bottom. As a result, resist patterns formed by a chemically amplified resist will have a deteriorated form and will provide poor resolution. This ill-affects subsequent steps.
The above-described problem becomes more serious especially when forming a resist pattern on a basic semiconductor substrate covered with a TiN film or SiN film. However, such a problem may be produced even to a non-basic semiconductor substrate.
U.S. Pat. No. 5,219,788 tries to provide a solution to the aforesaid problem by forming a thin film on top of a semiconductor substrate and then forming a resist pattern on the thin film with a chemically amplified resist.
Another method of washing a semiconductor substrate surface with a solution of acid to get rid of surface contaminants has been used widely.
U.S. Pat. No. 5,219,788 still has the drawback that the process becomes complicated thereby increasing the production cost.
The latter method, too, still has the drawback that it cannot perfectly prevent the occurrence of footing or scumming and under-cutting. It is difficult for this method to prevent the occurrence of footing or scumming and under-cutting for the case of a basic semiconductor substrate with its surface covered with a TiN or SiN film.